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I guess I am uneasy with this analysis - unless you can show that mankind has searched most of the planet for more phosphorous and come up empty, then it seems entirely possible that current reserves are only limited because nobody has bothered to go out and look for more.
The curves show a plateau in total production, but is that because it gets harder and harder to find more phosphorous, or is it because improved agricultural techniques to minimize topsoil losses and to reduce nutrient runoff have reduced the demand for more phosphorous?
I share the same concerns. Do we have discovery data for phosphorous deposits? I was wondering if a discovery peak exists. The use of phosphorus has also been limited in certain country (ex: France) because of problems of eutrophication of water.
It seems intuitive that the phosphorus deposits have to be very easy to access for it to be profitable. Phosphate rock goes for around $30 per ton, while a barrel of oil is about $70 for 0.136 tons (or $500/ton). That must have some impact on how far and deep we will go to recover it ... at the present time.
I think you can rule that out, because the phosphorous is used by the plants to build themselves. It's a cycling element, not a catalyst, so it needs to be renewed after every harvest. A typical ecology keeps it local via dropping leaves, faeces and animal corpses. However, if you harvest and export it, it is necessary to supply new P from either a finite source (mineral deposits or the soil), or import it from elsewhere, preferably from those that consumed it in the first place, to close the cycle.
The very fact that runoff and rivers have problems with eutrophication suggests that excess phosphorous has been over-applied, and is washing into various waterways. As humans become smarter about preventing this, then demand for phosphorous would go down.
Eventually you would reach a theoretical point where the only phosphorous that is applied is used by the plants that are shipped out, but even then some of it is recoverable from sewage.
I think you are correct that farmers are becoming better at managing fertilizer application. Have world sales of phosphate decreased because of greater use efficiency, or are sales still rising with previously mined phosphates stores being depleted to compensate for lower extraction rates?
Another reason for run off problems, in addition to over application, could be the type of phosphate applied. I believe those superphosphate products have been manipulated to increase solubility and rapid availability to plants, but since the soils are mostly dead and organic matter levels are so low, any excess phosphate runs off fast.
Organic farmers use products that are less immediately available, have slow release properties, and therefore don't have these run off problems.
In areas with low soil PH, runoff is more unlikely. In soil conditions with a PH of say... under 5.3, P tends to bond with soil particles, more so in fine/clay soils which have more surface area per gram.
Liquid calcium or Lime will raise the PH and make the "P" water soluble again.
N,P, K & Fe are not water soluble at low PH. So the mechanism of runoff should be of low concern in soils with PH below 5.3 or so.
See: cation exchange capacity
Conveniently, Fertilizers lower the pH. If the pH goes below 4.5, then the plants suck up potential heavy metals (and I don't mean Black Sabbath). Below 3.5 pH, Aluminum becomes soluble and everything dies.
Expanding further, the fungus and bacteria association with the plant diminishes with these fertilizers (and much soil life is killed). The plants become bloated with water, which the herbivore insects take note and feast. Then the insecticides kill these "pests", but also the insect life in the soil. Without the insects to burrow into the soil, bringing down fungi, bacteria, and protozoa to the roots, the soil goes anaerobic.
Anaerobic soil means low pH, so even applications of Lime or whatnot don't work for long, as the nutrient plugs are already gone, the bacteria fight to keep a low pH, and nutrients wash out. Even worst are the blights that can now infiltrate an unprotected ecosystem (note fungi above).
http://soils.tfrec.wsu.edu/mg/chemical.htm
Aluminum starts becoming water soluble at 6.0 and lower.
PH of 4.5 is a bit too late, the nitrogen ammonia cycle is basically stopped at 4.5. At a PH of 5.6 nitrogen fixation by plants starts to be problematic.
Water logged soil is anaerobic, re: lack of oxygen.
Off topic but still an energy post. Both heavy duty and alkaline batteries use carbon and zinc electrodes but heavy duty batteries use an acid electrolyte and alkaline batteries use (you guessed it) potassium hydroxide. Alkaline batteries are mucho superior in every respect except initial cost and I never knew why until I saw your post. You do NOT want your electrode, in this case zinc, dissolving in your electrolyte.
Nickel Iron batteries, touted by one of us, last essentially forever because the electrodes are essentially insoluble in potassium hydroxide. They have other issues, but they last forever.
I shoulda known quoting from my Permaculture class. However, the pH and Aluminum problem is still around 3.5 pH when no plant can survive. The issue relates to the interaction between Phosphorus and Aluminum across a spectrum of pH.
http://www.plantphysiol.org/cgi/reprint/18/4/708.pdf
I'm sure there are other references out there.
Yes, water logged soil is indeed anaerobic. I'm trying not to write a book inside a comment, so have compressed the whole process of tilling, fertilizing, biocides, etc that comprise our conception of food "production" as fundamentally flawed and always ends in depleted soil and desertification.
PH of 4.5 is a bit too late
Let's not split hairs to fill in the 0.5 pH to go. It's out there, if you want to find a plant that "survives" it. However, below 3.5 is certainly a dead zone.
Stream of consciousness. Nobody thinks without phospourus. Aluminum causes phospourus to precipitate. Aluminum is implicated in Alzheimers.
Blood is a mild base. Unless you suffer from acidosis. CO2 makes carbonic acid. Therefore exercise is bad for you. Couch potatoes have the best brains on the planet.